Substrate heating method, substrate heating system, and applying developing system

ABSTRACT

With respect to a substrate on which a resist solution is applied, the inplane uniformity of the quality of a resist film is improved in a heating processing carried out before exposure, and the yields of products are improved. A substrate on which a resist solution is applied is mounted on a heating plate in a processing vessel. Then, a purge gas is supplied into the processing vessel, and heating is started. Above the mounting position of the substrate, a thickness detecting sensor for monitoring the thickness of the resist film formed on the surface of the substrate is provided. When the thickness becomes a predetermined value or less, a control part cause a lift pin to upwardly move so as to increase the distance between the substrate and the heating plate. Thus, the heating value applied to the substrate decreases, and thereafter, only the solvent is volatilized without having a bad influence on a polymer in the resist film.

TECHNICAL FIELD

The present invention relates generally to a substrate heating methodand system for volatilizing a solvent from the surface of a substrate,on which a resist solution is applied, by heating the substrate, and anapplying and developing system to which the substrate heating system isapplied.

BACKGROUND ART

In processes for producing semiconductor devices and LCDs, a resistprocessing to a processing substrate is carried out by a techniquecalled photolithography. This technique is carried out by a series ofsteps of applying a resist solution on, e.g., a semiconductor wafer(which will be hereinafter referred to as a wafer), to form a liquidfilm on the surface of the wafer, exposing the resist film by a photomask, and thereafter, carrying out a developing processing. In suchsteps, twice heating processes called PAB (Post Applied Bake) and PEB(Post Exposure Bake) are carried out before and after the exposureprocessing. The heating processing in the PAB uses a system shown in,e.g., FIG. 8.

This system comprises a heating plate 14 including a heater 13 in aprocessing vessel 1 which comprises a lower portion 11 and a lid 12. Onthe heating plate 14, protrusions 15 are provided. When a semiconductorwafer (which will be hereinafter referred to as a wafer) being asubstrate is held in a horizontal attitude to be mounted on the heatingplate 14, a gap of a very small distance, e.g., 0.1, is formed betweenthe wafer W and the surface of the heating plate 14 so as to preventparticles from adhering to the surface of the heating plate 14. The lid12 is connected to a gas supply pipe (not shown) for supplying, e.g., apurge gas of a room temperature, into the processing vessel 1 and to anexhaust pipe (not shown) for exhausting from the processing vessel 1.These serve to form an air flow in the vicinity of the surface of thewafer W during a process to prevent a temperature distribution frombeing caused on the surface.

The control of the temperature of the wafer W in the above describedsystem is carried out by detecting the temperature of the surfaceportion of the heating plate 14 by means of a temperature sensor 16,feeding back a detected signal to a control system 17, and controllingthe power of the heater 13 so that the temperature of the surfaceportion of the heating plate 14 is held at a predetermined processtemperature Various conditions during the process are constant until theend of the process from the start thereof. Specifically, the wafer W isheated to, e.g., 100° C., and this state is continued for 90 seconds tocomplete the processing.

By the way, the inventor has grasped that the line width of a resistpattern finally formed on the surface of the wafer W varies whenprocessing conditions vary in the PAB if a certain resist (e.g.,KrF-acetal) is used. Therefore, the PAB has some influence on thequality of the resist film. However, it has not been understood how toview the processing conditions to stabilize the quality of the resistfilm.

As described above, the object of the PAB is to heat (bake) the wafer W,on which the resist solution is applied, before exposure to volatilize apredetermined amount of a solvent contained in the resist solution.Therefore, the inventor has noticed the heating time to examine thecorrelation between the heating time and the resist film after theprocessing, and has noticed characteristics (Rmin) of the resist film tolearn that there is a predetermined correlation between thecharacteristics of the resist film and the heating time. The Rmin showsa thickness h1 (see FIG. 9( a)) of a dissolved resist film when adeveloping solution is supplied to an unexposed resist film which hascompletely heated in the PAB, and means that, as the value of h1 issmaller, the resist film is more stable to the developing solution, sothat the inplane uniformity of the quality of the film is higher toincrease the inplane uniformity of the line width.

Then, as shown in a characteristic diagram of FIG. 9( b), the value ofRmin is lowest at a heating time of t0, and a V shape is drawn about thelowest value. The reason why the value of Rmin thus varies is consideredthat the resist film is not substantially solidified (not stabilized)until to since the heating time is short. The Rmin after t0 isconsidered as follows. That is, since the decrease of the resist filmduring baking is mainly caused by the volatilization of the solvent, thetotal amount of a polymer forming resist components contained in theresist solution does not vary as shown in, e.g., FIG. 10( a), and theproportion of the polymer in the whole resist film gradually increases.On the other hand, heating conditions are constant as described above,the proportion of thermal energy received by the polymer increases asthe thickness of the film decreases as shown in, e.g., FIG. 10( b). Theexcessive supply of thermal energy to the polymer causes thedecomposition of a protective group of the polymer and the variation ofthe formation of the polymer. This is considered to increase the Rmin.

The foregoing suggests that the quality of the film can be optimized bychanging the heating value applied to the resist film in accordance withthe amount of vilatilized solvent. However, since the ununiformity ofthe quality of the film can be eliminated by the conventional techniquefor always baking on constant process conditions regardless of thecomponents of the resist film, the inventor has searched for a newheating method in the PAB.

DISCLOSURE OF THE INVENTION

The present invention has been made in such circumferences, and it is anobject of the present invention to provide a technique capable ofimproving the inplane uniformity of the quality of a resist film in aheating processing, which is carried out before exposure, with respectto a substrate on which a resist solution is applied. It is anotherobject of the present invention is to improve the yields of productswhen a substrate heating system for carrying out the same heatingprocessing as that in the present invention is applied to an applyingand developing system.

According to the present invention, there is provided a substrateheating method for heating a substrate, on which a resist solution isapplied, in a processing vessel, the method comprising: a first step ofapplying thermal energy to the substrate to volatilize most of a solventin the resist solution; and then, a second step of causing a heatingvalue, which is applied to the substrate for a unit time, to be smallerthan that at the first step to volatilize the solvent remaining in theresist film.

According to such a method, the heating value applied to the substratecan be changed in accordance with the variation in component of theresist solution when the substrate is heated, so that it is possible toenhance the inplane uniformity of the quality of the resist film.Specifically, it is possible to adapt a technique for previouslygrasping, e.g., the timing in changing the step between the first andsecond steps, on the basis of Rmin being an index of determination ofthe inplane uniformity of the film, monitoring the amount of thedecrease of the thickness (the rate of the decrease of the thickness)during the heating processing, and using a switching timing when therate is a predetermined value or less.

As the method for changing the heating value applied to the substrate,there are preferably used a method for causing the heating value appliedto the substrate for a unit time, to be smaller than that at the firststep by increasing the distance between the substrate and the heatingplate as compared with that at the first step a method for decreasingthe temperature of the heating plate by decreasing the power supplied toa resistance heating element provided in the heating plate, and a methodfor decreasing the temperature of the heating plate by supplying arefrigerant to the heating plate, when the substrate is mounted on theheating plate to heat the substrate by the heating plate. When a purgegas is supplied into a processing vessel, there may be used a method forchanging the temperature of the purge gas. Furthermore, it is notrequired to monitor the amount of the decrease of the thickness of theresist solution in real time. For example, the timing in which the rateof the decrease of the thickness of the resist solution is small may bepreviously grasped, and the first and second steps may be changed inthat timing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a preferred embodiment of asubstrate heating system according to the present invention;

FIG. 2 is a graph showing operation in the preferred embodiment;

FIG. 3 is a graph showing operation in the preferred embodiment;

FIG. 4 is a graph showing another preferred embodiment of a substrateheating system according to the present invention;

FIG. 5 is a schematic diagram for explaining a further preferredembodiment of a substrate heating system according to the presentinvention;

FIG. 6 is a plan view showing an example of an applying and developingsystem including the substrate heating system;

FIG. 7 is a perspective view showing an example of an applying anddeveloping system including the substrate heating system;

FIG. 8 is a schematic illustration showing a conventional substrateheating system;

FIG. 9 is a schematic illustration for explaining the problem to besolved by the invention; and

FIG. 10 is a schematic illustration for explaining the problem to besolved by the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to the longitudinal sectional view of FIG. 1, a preferredembodiment (a first preferred embodiment) of a substrate heating systemaccording to the present invention will be described below. In thissystem, a housing 100 houses therein a processing vessel 20 comprising alower portion 22, the lower portion of which is supported on a legportion 21, and a lid 3 which is vertically movable above the lowerportion 22. In the side face of the housing 100, an opening portion Efor carrying a wafer W being a substrate in and out of the housing 100is formed. This processing vessel 20 will be described from the lowerportion. Inside of the lower portion 22, a heating plate 23 being acylindrical heating plate is provided. Between the internal wall face ofthe lower portion 22 and the external wall face of the heating plate 22,a recessed portion 24 is formed all around. The heating plate 23 servesas a supporting plate for the wafer W, and is made of, e.g., aluminumnitride (AlN).

In the vicinity of the surface (top face) of the heating plate 23,heaters 25 being a plurality of divided resistance heating elements, anda thermocouple TC being a temperature detecting means are buried.Temperature data obtained by the thermocouple TC are transmitted to acontrol part 4. The control part 4 is designed to control the electricenergy, which is supplied to the heaters 25 via a power supply part 25a, on the basis of the temperature data. On the surface of the heatingplate 23, three protrusions 26 having a height of, e.g., 0.1 mm, areprovided at regular intervals in circumferential directions. The wafer Wbeing a substrate is horizontally supported on these protrusions so asto be slightly spaced from the surface of the heating plate 23. Belowthe position at which the wafer W is supported, for example, three liftpins 27 are retractably provided so as to path through the heating plate23. The lift pins 27 serve to deliver the wafer W between a wafertransfer arm (not shown) and the heating plate 23, and also serve tocontrol the heating value, which is applied to the wafer W, bycontrolling the height during the process (the details thereof will bedescribed later). For example, the height of the lift pins 27 can bechanged by means of a lifting mechanism 28 which is a lifting meanscomprising a linear motor (not shown) and a supporting member 27 a. Thecontrol of the driving of the driving mechanism 28 is carried out by thecontrol part 4.

The upper portion of the processing vessel 20 will be described below.The lid 3 is vertically movable by a lifting member 31 connected to adriving mechanism (not shown). When the wafer W is heated, the bottomend of the lid is fitted into the recessed portion 24 to surround thewafer W. The lid 3 is connected to a gas supply pipe 32 being a purgegas supply means and an exhaust pipe 33, to supply a purge gas, such asnitrogen gas or air, into the processing vessel 20 from the gas supplypipe 32 via gas holes 34 and 35 and to exhaust the gas from the exhaustpipe 33 via an outlet 36 so as to be capable of forming an air flow onthe surface of the wafer W (see arrows in the figure). The lid 3 isprovided with a thickness detecting sensor 37 being a thicknessmonitoring means which passes through, e.g., the ceiling portion of thelid 3, so that the tip of the thickness detecting sensor 37 faces thewafer W. Thickness data of a resist film on the surface of the wafer Ware transmitted to the control part 4. The thickness detecting sensor 37is vertically movable by means of a positioning mechanism 38 so as to becapable of being spaced from, e.g., the wafer W by a predetermineddistance, and the control thereof is carried out by the control part 4.The thickness detecting sensor 37 is an optical thickness detectingsensor for measuring the thickness by detecting reflected light from theliquid film.

As the thickness monitoring means, a solvent concentration detectingmeans may be used in place of the thickness detecting sensor 37. In thiscase, since the thickness decreases as the amount of volatilized solventincreases, the thickness can be known by detecting the concentration ofthe solvent.

By the way, the flow rate of the purge gas supplied into the processingvessel 20 via the gas supply pipe 32 is controlled by the control part 4although it is not shown. That is, the control part 4 is designed tocollectively control the flow rate of the purge gas and the temperatureof the heaters 25. Such control is carried out in accordance with, e.g.,a recipe which is prepared in accordance with the kind of the appliedfilm and which is read from a memory 41.

The operation of the above described preferred embodiment will bedescribed below. First, while the lid 3 is lifted by the drivingmechanism (not shown), a wafer transfer arm (not shown) moves above theheating plate 23 via a gap between the lid 3 and the lower portion 22,and the wafer W is horizontally supported on the lift pin 27 protrudingfrom the lower side. Then, when the lift pin moves downwards, the waferW is horizontally supported on the protrusions 26. Then, when the lid 3is moved downwards, a processing space for the wafer W is formed so asto be surrounded by the lid and the lower portion. Thereafter, inaccordance with the predetermined recipe as described above, the heatingby the heaters 25, and the supply and exhaust of a purge gas, e.g., N₂(nitrogen) gas, into and from the processing vessel 20 are started.

At this time, the lift pin 27 is in a state that the lift pin 27 iscompletely buried below the surface of the heating plate 23, i.e., thewafer W is positioned at a height (first distance) of 0.1 mm from theheating plate 23, and the thickness detecting sensor 37 is positionedabove the surface of the wafer W by, e.g., 5 mm to 10 mm. In this state,thickness data for the resist film on the surface of the wafer W arecontinued to be transmitted to the control part 4. Furthermore, thewafer W is moved upwards by the lift pin 27 in accordance with theproceeding of the heating process as will be described later. The heightof the thickness detecting sensor 37 may be controlled by thepositioning mechanism 38 in accordance with the upward movement. Forexample, the height may be controlled so that the distance from thewafer W is constant.

At the beginning of the starting of the heating, most of the heatingvalue applied to the wafer W is used for volatilizing the solvent in theresist film, so that the thickness rapidly decreases as shown in thecharacteristic diagram of FIG. 2. However, as described “Problem to besolved by the Invention”, since excessive heating value is applied tothe polymer contained in the resist after a certain time, the heatingvalue applied to the wafer W is controlled so as to be decreased. The“certain time” corresponds to t0 shown in FIG. 9( b), and t0 isdetermined by the amount of the decrease of the thickness per unit time(which will be hereinafter referred to as a thickness decreasing rate).This can be calculated by dividing the value (a1−a2) of the decrease ofthe thickness between the times b1 and b2 by (b2−b1) as shown in, e.g.,FIG. 3. This value decreases as the elapse of time as can be seen fromthe shown curve.

By the way, the relationship between the time of t0 and the thicknessdecreasing rate is previously grasped by the relationship between FIGS.9( b) and 10(b). Assuming that a step before the time of t0 is a firststep and a step after to is a second step, the second step is a step ofsuccessively volatilizing the solvent in the resist film whileinhibiting excessive heating value from being applied to the polymer bydecreasing the heating value (thermal energy per unit time applied tothe wafer W. Therefore, if the control part 4 grasps that the timereaches t0, i.e., when the amount of the decrease of the thicknesscalculated on the basis of the detected value of thickness from thethickness detecting sensor 37 is lower than a preset value, the controlpart 4 gives a command to the lifting mechanism 28 so that the heatingvalue applied to the wafer W decreases to a predetermined value, to movethe lift pin 27 upwards. The relationship between the height of the liftpin and the heating value applied to the wafer W for a unit time hasbeen previously grasped on the basis of the heating pattern of theheaters 25 which is recorded in the recipe, and the lift pin 27 movesupwards to the height P1 (second distance) on the basis of the data.

The height P1 of the lift pin 27 at the time of to is set so that theheating value applied to the wafer W for a unit time is slightly lowerthan, e.g., a limit value at which the polymer protective group isdecomposed. After the value of the heating value approaches the limitvalue at the time of t1 again, the heating value applied to the wafer Wis decreased while the lift pin 27 is gradually moved upwards. After thelift pin 27 is moved upwards once at the time of t0, the height may befreely changed in accordance with the variation in temperature and thecontents of the processing. Therefore, while the lift pin 27 has beengradually moved upwards after the time of t1 as an example, the lift pin27 may be moved downwards, or may be moved upwards after being moveddownwards once.

Thus, the wafer W moves upwards (or downwards) between a distance of 0.1mm from the heating plate 23 (a state that the lift pin 27 does not moveupwards) and a distance of, e.g., 25 mm from the heating plate 23, andafter the process is completed, the wafer W is carried out of theprocessing vessel 20 by the reverse procedure of that during thecarrying-in.

As described above, according to this preferred embodiment, therelationship between the index (Rmin) indicative of the inplaneuniformity of the quality of the resist film formed on the surface ofthe wafer W and the heating time for the wafer W in the PAB is noticed,and the height of the wafer W is changed in accordance with thethickness decreasing rate of the resist film to control the heatingvalue applied to the resist film, so that it is possible to optimize thequality of the resist film. That is, large thermal energy is applied topromote volatilization until most of the solvent is volatilized, andthereafter, excessive heating value is prevented from being applied tothe protective groups and polymer while the remaining slight solvent isvolatilized, so that it is possible to ensure a good quality of filmwhile rapidly carrying out heating (backing). In addition, since thereis a correlation between the inplane uniformity of the quality of theresist film and the precision of the line width of the resist patternobtained after exposure being a post-processing as described above, aresist pattern having a high precision of line width can be obtainedfrom the optimized resist film.

Moreover, when a plurality of processes are sequentially carried out,the processes are conventionally carried out so as to be always aconstant heating pattern, whereas thermal energy applied to the resistfilm is changed in accordance with the variation in component of theresist film in this preferred embodiment. Therefore, the processing ofany one of the wafers W can be optimized, so that it is possible toimprove yields.

Furthermore, the technique for controlling thermal energy applied to thewafer W during the heating in this preferred embodiment should not belimited to a technique that the distance between the wafer W and theheating plate 23 is changed as described above. For example, the sameeffects can be obtained by changing the surface temperature of theheating plate 23 as the second preferred embodiment which will bedescribed below.

In this preferred embodiment, the control of the temperature of theheating plate 23 is intended to be realized by controlling the electricenergy supplied to the heaters 25. FIG. 4 is a characteristic diagramshowing the relationship between the variation in thickness when aheating process is carried out and the temperature of the heating plate23 (the temperature of the thermocouple TC). As shown in the figure, thecontrol part 4 maintains the temperature of the heating plate 23 at atemperature of Q1 (a first temperature) at a first step to positivelyvolatilize the solvent, and grasps the timing of t0 on the basis ofthickness data obtained by the thickness detecting sensor 37 similar tothe above described preferred embodiment, to decrease the output valuein the power supply part at the time of t0 to change the step to asecond step.

Then, the temperature of the heating plate 23 suddenly decreases to be atemperature of Q2 (a second temperature), which is lower than Q1 by,e.g., 10° C. to 20° C., at the time of t2 to be maintained as it is.When the process is completed at the time of t3, the control part 4raises the temperature of the heaters 25 until the temperature of theheating plate 23 is equal to the temperature Q1 at the first step, andprepares the next processing to carry the processed wafer W out of theprocessing vessel 20 and to carry a new unprocessed wafer in, tosimilarly repeat the heating for a predetermined number of wafers. Themethod for changing the surface temperature of the heating plate 23should not be limited to the control of the electric energy to theheaters 25. For example, a refrigerant passage (not shown) is formed inthe heating plate 23 to cause a refrigerant to flow in an appropriatetiming so that the surface temperature of the heating plate 23 issimilar to that in FIG. 4. Alternatively, a cooling gas for causing arefrigerant to contact the reverse of the heating plate 23 may besupplied.

If the control of thermal energy applied to the wafer W is carried outby changing the temperature of a purge gas, the same effects as those inthe above described example can be obtained. FIG. 5( a) is a schematicillustration showing a purge gas supply system in this third preferredembodiment. In this preferred embodiment, a temperature control part 51capable of changing the temperature of a purge gas, e.g., air, between0° C. and 30° C., and a flow meter 52 are provided in order thereof fromthe upstream in the middle of the gas supply pipe 32 in the firstpreferred embodiment. FIG. 5( b) is a characteristic diagram showing thevariation in thickness and the variation in temperature of the purge gasin this preferred embodiment. First, the control part 4 determines thetime of t0 on the basis of thickness data while maintaining thetemperature of the purge gas at R1 at the step of t0, and suddenlydecrease the gas temperature in the temperature control part 51 on thebasis of the flow rate of the purge gas obtained from the flow meter 52,at the time of t0. Then, at the time of t4 at which the temperature ofthe purge gas decreases to R2, the temperature of the gas is maintainedas it is. When the processing is completed, the gas temperature isreturned to R1, and the next unprocessed wafer W is prepared to becarried in. Furthermore, since the heating value applied to the wafer Wper unit time may be decreased after the time of t0, the suppliedheating value may be controlled by combining the temperature of thepurge gas with the flow rate thereof.

While the time of t0 has been determined in real time in the abovedescribed preferred embodiment, the control part may change the controlfrom the first step to the second step at a certain time on the basis ofpreviously acquired data. In this case, a dummy wafer may be used forcarrying out a heating process while measuring the variation inthickness of the resist film by means of, e.g., a thickness detectingsensor, and for deriving a time, at which most of the solvent in theresist solution is volatilized, on the basis of data of the variation inthickness decreasing rate, and that time may be stored in a memory.Thereafter, a wafer W for product is used for carrying out a heatingprocess on the basis of the calculated results without measuring thethickness. Here, the sentence “most of the solvent in the resistsolution is volantized” means favorably that 50%–98% of the solvent inthe resist solution is volantized, but more realistically that 50%–80%of the solvent in the resist solution is volantized.

The terms “first temperature”, “second temperature”, “first distance”and “second distance” in claims should not mean that they are alwaysconstant values, and include cases where the values gradually change.That is, for example, in the second preferred embodiment, thetemperature Q1 corresponding to the first temperature may change betweenthe starting of the heating and the time of t0 so long as it ismaintained to be higher than the temperature Q2 corresponding to thesecond temperature. Specifically, the temperature Q1 may graduallydecrease before t0, and suddenly decrease after the time of t0.

Finally, referring to FIGS. 6 and 7, an example of an applying anddeveloping system including the above described substrate heating systemas a unit will be described below. In the figure, S1 denotes a cassettesupporting part for carrying a cassette C housing therein a pluralityof, e.g., 13, wafers, in and out. The cassette supporting part isprovided with a supporting table 61 capable of supporting thereon aplurality of cassettes C, and a delivery means 62 for taking the wafersW out of the cassettes C.

Inside of the cassette supporting part S1, a processing part S2surrounded by a housing 70 is provided. This processing part S2 isalternately provided with shelf units U1, U2 and U3 includingheating/cooing units including the above described substrate heatingsystem as multi stages, and main transfer means 71A, 71 b for deliveringthe wafers W between the respective processing units including anapplying/developing unit which will be described below. That is, theshelf units U1, U2, U3 and the main transfer means 71A, 71B are alignedin longitudinal directions as being viewed from the cassette supportingpart S1, and each of connecting portions is provided with a wafercarrying opening portion (not shown), so that the wafer W can freelymove in the processing part S1 from the shelf unit U1 at one end to theshelf unit U2 at the other end. The main transfer means 71A and 71B arearranged in a space surrounded by partition walls 72 which comprise oneface portion on the side of the shelf units U1, U2 and U3 arranged inlongitudinal directions as being viewed from the cassette supportingpart S1, one face portion on the side of liquid processing units U4 andU5 which are arranged on, e.g., right side, and which will be describedlater, and a back face portion being one face on the left side. In thefigure, reference numbers 73 and 74 denote a temperature/humiditycontrol unit having a processing solution temperature control unit and atemperature/humidity control duct which are used for each unit.

As shown in, e.g., FIG. 7, the liquid processing units U4 and U5comprise a housing portion 75 defining a space for supplying chemicals,such as applying solution (resist solution) and developing solution, andan applying unit COT, a developing unit DEV and a reflection preventingfilm forming unit BARC which are stacked on the housing portion 75 in aplurality of stages, e.g., 5 stages. In the above described shelf unitsU1, U2 and U3, various units for carrying out a pre-processing and apost-processing before and after the processing carried out by theliquid processing units U4 and U5 are stacked in a plurality of stages,e.g., 10 stages.

Inside of the shelf unit U3 in the processing part S2, an exposure partS4 is provided via an interface part S3. The interface part S3 comprisesa first transfer chamber 76 and a second transfer chamber 77 which areprovided between the processing part S1 and the exposure part S4. Theinterface part S3 includes two delivery means 78 and 79, a shelf unit U6and a buffer cassette C0, so as to be capable of carrying a wafer W,which is arranged in, e.g., the shelf unit U6, and on which an applyingsolution is applied, in a route of delivery means 78→shelf unitU6→delivery means 79→exposure part S4. The exposed wafer W is returnedto the processing part S2 in the reverse route, and stored in thecassette C after being developed.

As described above, according to the present invention, it is possibleto improve the inplane uniformity of the quality of the resist film withrespect to the substrate, on which the resist solution is applied, inthe heating processing carried out before exposure. According to anotherinvention, it is possible to improve the yields of products when thesubstrate heating system for carrying out the same heating processing asthat in the present invention is applied to an applying and developingsystem.

1. A substrate heating method for heating a substrate, on which a resistsolution is applied, in a processing vessel, the method comprising: afirst step of applying thermal energy to a substrate to volatilize mostof a solvent in a resist solution; and a second step of causing aheating value, which is applied to the substrate for a unit time, to besmaller than that at the first step to volatilize the solvent remainingin a resist film, wherein a liquid film of the resist solution ismonitored by thickness monitoring means, and the first step is changedto the second step when the amount of decrease of thickness of theliquid film per a unit time is changed to a small value.
 2. A substrateheating method as set forth in claim 1, wherein said substrate isarranged on a heating plate, and a distance between the substrate andthe heating plate at the second step is longer than that at the firststep, so that the heating value applied to the substrate for the unittime at the second step is smaller than that at the first step.
 3. Asubstrate heating method as set forth in claim 1, wherein said substrateis arranged on a heating plate, and a temperature of the heating plateat the second step is lower than that at the first step, so that theheating value applied to the substrate for the unit time at the secondstep is smaller than that at the first step.
 4. A substrate heatingmethod as set forth in claim 3, wherein the temperature of the heatingplate is decreased by decreasing a power supplied to a resistanceheating element provided in the heating plate.
 5. A substrate heatingmethod as set forth in claim 3, wherein the temperature of the heatingplate is decreased by supplying a refrigerant to the heating plate.
 6. Asubstrate heating method as set forth in claim 1, wherein a purge gas issupplied into the processing vessel, and a temperature of the purge gasat the second step is lower than that at the first step, so that theheating value applied to the substrate for the unit time at the secondstep is smaller than that at the first step.
 7. A substrate heatingmethod as set forth in claim 1, wherein said thickness monitoring meansis an optical thickness detecting sensor.
 8. A substrate heating methodas set forth in claim 1, wherein said thickness monitoring means issolvent concentration detecting means for detecting a concentration ofthe solvent in the liquid film.
 9. A substrate heating method forheating a substrate, on which a resist solution is applied, in aprocessing vessel, the method comprising: a first step of applyingthermal energy to a substrate to volatilize most of a solvent in aresist solution; and a second step of causing a heating value, which isapplied to the substrate for a unit time, to be smaller than that at thefirst step to volatilize the solvent remaining in a resist film, whereina timing in changing of a thickness decreasing amount per unit time to asmall value with respect to a liquid film of the resist solution ispreviously grasped, and the first step is changed to the second step inthat timing.